All excellent points as usual, Glen. And of course, I was looking at this with little more than an entertaining comment to make - I would imagine with enough analysis of specific users who download your content, you'd be able to figure out (to an extent), all the different trends you mentioned:
1) Visitors who come once, download and try your material, and then never come back again / don't sign up for a mailing list, etc
2) Visitors who come once, download and try your material, and then return on occassion looking for new content / sign up for said mailing list, and actually access new content as it is made available
Each of these is contingent on your releasing new material, as you say - even if person 2 likes your stuff, and you let your site stagnate, they will eventually stop coming since they will assume you just don't post new content anymore.
One other thing that might simply be a problem for some is that the music they play is either not listened to much by Internet users who actively seek online music content, or is not a popular genre amongst any particular groups of people in modern culture. The former is probably more likely than the latter, since there is someone who will enjoy just about any type of content, and if that type of content was ever a somewhat widely popular genre, it is even more likely that someone will like it if its any good.
We will skip the notion that the content has to actually have some sort of intrinsic quality before people will enjoy it (and quality can mean many things - Britney Spears is "quality" if you are looking for a teen pop singer who performs generic music).
Beyond the fact that my stuff may be awful, I don't know how much of an audience there is acoustic folk music these days, and that seems to be what my material falls most closely under. So who knows - guess we'll have to wait and see
Also, I have in fact used that site you mentioned - it brings you to some entertaining stuff, and I think its interesting that you got some hits from it. I'll have to keep it in mind when I finally muster the creative drive to finish the lyrics to a number of songs I'm working on, and then finally muster the courage to get torn a new one by the Internet community at large
